User`s guide

4 User’s Guide
Signal Studio for WiMAX E4438C Option H13
About WiMAX
About WiMAX
Introduction
WiMAX is designed for point-to-point and point-to-multipoint systems to deliver
high-speed data services. Applications include providing backhaul for wireless LAN
hot-spots or cellular base stations, replacing T1 lines to enterprises and providing wireless
DSL service to homes and businesses. Although the 802.16-2004 standard covers operation
up to 11 GHz, the WiMAX Forum is focused on deployments in the 2.5 GHz, 3.5 GHz and 5
GHz bands.
Base stations (BS) transmit downlink (DL) signals to one or more subscriber stations (SS),
also referred to as consumer premises equipment (CPEs). The SS transmit uplink signals
back to the base stations.
Overview of Frame Structure
The WirelessMAN-OFDM physical layer (PHY) supports a frame-based transmission. In
licensed bands, the duplexing method is either frequency division duplexing (FDD) or time
division duplexing (TDD). FDD SSs may also be half-duplex FDD (H-FDD). In
license-exempt bands, the duplexing method is TDD.
For time division duplex (TDD) mode, a frame consists of a downlink subframe and an
uplink subframe, as shown in Figure 1 on page 5. A downlink subframe consists of only one
downlink PHY protocol data unit (PDU). An uplink subframe consists of contention
intervals scheduled for initial ranging and bandwidth request purposes and one or
multiple uplink PHY PDUs, each transmitted from a different SS. In general, users will
create either the downlink or uplink signal in the Signal Studio for WiMAX software, with
a gap to cover the time for the other portion of the transmission.
A downlink PHY PDU starts with a long preamble, which is used for PHY synchronization.
The preamble is followed by a frame control header (FCH) burst. The FCH contains a
DL_Frame_Prefix (DLFP) to specify burst profile and length of one or several downlink
bursts immediately following the FCH. There is a DLFP editor available in the software.
The FCH may be followed by broadcast messages such as a downlink map (DL-MAP)
message and/or uplink map (UL-MAP) message, then uplink channel descriptor (UCD)
and downlink channel descriptor (DCD) messages. Signal Studio for WiMAX does not
currently support creation of these messages, but the user can include them as a user data
file.
The FCH is followed by one or more downlink data bursts, each transmitted with different
burst profile. Data bursts with more robust modulation types are transmitted before
bursts with less robust modulation (e.g. a QPSK burst is transmitted before a 64QAM
burst).
The uplink subframe consists of a contention slot for initial ranging and a contention slot
for bandwidth requests, followed by uplink PHY PDUs from individual subscriber stations.
Each UL PHY PDU consists of a short preamble followed by a data burst, which includes a
MAC header, payload data and CRC.